1. Field of the Invention
The present invention relates to optical-electronic systems in which optical interconnects are used to distribute signals to or between one or more integrated circuit devices.
2. Description of the Related Art
Many modern integrated circuits are reaching limits on heat generation and adequate signal propagation, at least in part due to problems with interconnects. Advanced microprocessors are a good example. Signals are often carried within advanced microprocessors using copper wiring lines having lateral dimensions of substantially less than one micron. The resistance and density of these lines and the current carried by these lines are sufficient to make the interconnects a significant source of heating in the integrated circuit. Power dissipation and the increased margins required by excessive operating temperatures are problems for current integrated circuits and future circuit development is threatened by these problems.
A different problem arises from the close spacing between the wiring lines and the dielectric constant of the insulating material between the wiring lines. The close spacing of wiring lines and the high dielectric constant of the dielectric material between the wiring lines leads to high levels of interline capacitive and inductive coupling. The capacitive and inductive coupling are another source of undesirable heating, with the consequent heat dissipation and higher operating temperatures causing a range of problems. A more significant problem is that these capacitive and inductive couplings limit the propagation speeds of these wiring lines and lead to signal distortions that can prevent signals from being recognizable to receiving circuits.
The problems that have arisen in integrated circuits have also arisen in larger systems. Switching speeds for buses in computer systems are getting high, so that motherboards for computer systems are exhibiting heating and signal distortion problems like those discussed above with respect to integrated circuits.
Optical interconnects have been used to a limited extent in current electronic circuits. For example, optical isolation devices are frequently used in mixed signal applications including in modems. These applications have been in specialized areas and have not lead to the widespread use of optical interconnect technology. In addition, there has recently been some suggestions of exchanging signals between chips using optical interconnect technology. These proposed applications are for “edge” interconnects, where the optical interconnects replace the leads and circuit board connections used to communicate between chips. These proposed optical interconnect technologies have not lead to the widespread adoption of optical interconnect technology in electronic systems.
Optical circuit technology has advanced considerably in recent years due to the increased prevalence of optical networks and switches. These advancements have produced optical multiplexers, modulators, detectors, in-line amplifiers and switches. Waveguides on various substrates have become widely available. Despite these advancements, electronic and optical circuits have not been integrated.